Method and apparatus for the reduction of upstream request processing latency in a cable modem termination system

ABSTRACT

Upstream requests such a bandwidth requests, are processed by CMTS out of order on a priority basis to reduce latency in responding to the request. Specifically, a cable modem termination system (CMTS) is connected to a plurality of cable modems by a cable plant. The CMTS has a burst receiver adapted to be connected to the cable plant to process upstream data packet units and bandwidth requests transmitted by the cable modems. Each packet includes a header that uniquely distinguishes the bandwidth requests from other data types. Packet data units are arranged in a first memory queue. Bandwidth requests are arranged in a second memory queue. The headers of the packets processed by the burst receiver are inspected as they arrive at the CMTS to determine if the packets are packet data units or bandwidth requests. Packet data units are routed to the first memory queue. Bandwidth requests are routed to the second memory queue. Bandwidth allocation MAP messages are generated from the bandwidth requests stored in the second queue and transmitted downstream to the cable modems. The packet data units stored in the first queue are coupled to a data output for further distribution.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of application Ser. No. 09/652,718,filed Aug. 31, 2000, now allowed, which is a nonprovisional ofprovisional application Ser. No. 60/151,665, filed Aug. 31, 1999, all ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to TDMA communication systems, and moreparticularly, to a method and apparatus for processing bandwidthrequests in a cable modem termination system (CTMS).

A CMTS processes various types of upstream data it receives from cablemodems attached to a hybrid fiber cable (HFC) plant. Included data typesare protocol data units (PDU) and requests from the cable modems forbandwidth, i.e., time slots, to transmit packet data units upstream tothe CMTS. Each data type is uniquely identified in a header transmittedas part of the data packets. Conventionally, a CTMS processes all thedata types in the order of receipt, irrespective of the data type.

SUMMARY OF THE INVENTION

According to the invention, some data types, particularly bandwidthrequests, are processed out of order on a priority basis to reducelatency in allocating bandwidth to requesting cable modems.Specifically, a cable modem termination system (CMTS) is connected to aplurality of cable modems by a cable plant. The CMTS has a burstreceiver adapted to be connected to the cable plant to process upstreamdata packet units and bandwidth requests transmitted by the cablemodems. Each packet includes a header that uniquely distinguishes thebandwidth requests from other data types.

Data packet units are arranged in a first memory queue. Bandwidthrequests are arranged in a second memory queue. The headers of thepackets processed by the burst receiver are inspected as they arrive atthe CMTS to determine if the packets are data packet units or bandwidthrequests. Data packet units are routed to the first memory queue.Bandwidth requests are routed to the second memory queue. Bandwidthallocation MAP messages are generated from the bandwidth requests storedin the second queue and transmitted downstream to the cable modems. Thedata packet units stored in the first queue are coupled to a data outputfor further distribution.

As a result, bandwidth requests can be processed out of order and aheadof the data packet units so as to reduce latency in the allocation ofbandwidth to the cable modems.

DESCRIPTION OF THE DRAWINGS

The features of a specific embodiment of the best mode contemplated ofcarrying out the invention are illustrated in the drawings, in which:

FIG. 1 is a schematic diagram of a cable transmission system including aheadend with a cable modem termination system connected by a hybridfiber coaxial (HFC) network to a plurality of cable modems;

FIG. 2 is a schematic diagram of the headend and a cable modem in onehome of the cable transmission system shown in FIG. 1;

FIGS. 3 and 4 are diagrams of formats of bandwidth requests according tothe DOCSIS standard;

FIG. 5 is a functional block diagram illustrating how bandwidth requestsare processed according to the principles of the invention; and

FIG. 6 is a schematic block diagram of a CMTS and a coupled slave CMTSthat incorporates the invention,

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The disclosure of patent application Ser. No. 09/574,558, filed on May19, 2000 is incorporated fully herein by reference.

In a cable modem system, a headend or cable modem termination system(CMTS) is located at a cable company facility and functions as a modemwhich services a large number subscribers. Each subscriber has a cablemodem (CM). Thus, the cable modem termination system must be capable offacilitating bidirectional communication with any desired one of theplurality of cable modems.

As used herein, the cable modem termination system (CMTS) is defined toinclude that portion of a headend which effects communication with aplurality of cable modems. A typical cable modem termination systemincludes a burst receiver, a continuous transmitter and a medium accesscontrol (MAC).

The cable modem termination system communicates with the plurality ofcable modems via a hybrid fiber coaxial (HFC) network, wherein opticalfiber provides communication to a plurality of fiber nodes and eachfiber node typically serves approximately 500 to 2,000 subscribers.These subscribers communicate with the node via a shared coaxial cable.It is this sharing of the common coaxial cable which necessitates thatthe number of cable modems attached thereto be limited so as to mitigatethe likelihood of undesirable bit rate reductions which inherently occurwhen an excessive number of cable modems communicate simultaneously overa single coaxial cable.

The hybrid fiber coaxial network of a cable modem system utilizes apoint-to-multipoint topology to carry out communication between thecable modem termination system and the plurality of cable modems.Frequency domain multiple access (FDMA)/time division multiplexing (TDM)is used to facilitate communication from the cable modem terminationsystem to each of the cable modems, i.e., in the downstream direction.Frequency domain multiple access (FDMA)/time domain multiple access(TDMA) is used to facilitate communication from each cable modem to thecable modem termination system, i.e., in the upstream direction.

The cable modem termination system includes a downstream modulator forfacilitating the transmission of data communications therefrom to thecable modems and an upstream demodulator for facilitating the receptionof data communications from the cable modems.

Typically, the downstream modulator of the cable modem terminationsystem utilizes either 64 QAM or 256 QAM in a frequency band of 54 MHzto 860 MHz to provide a data rate of up to 56 Mbps. Since the upstreamchannel has a much lower data rate requirement, the upstream demodulatortypically uses either QPSK or 16 QAM in a frequency range of 5 MHz to 42MHz to provide a data rate of up to 10 Mbps.

The asymmetric data throughput defined by the upstream channel requiringa much lower data rate than the downstream channel results from theinherently larger amount of data which is communicated via thedownstream channel during pay-per-view, Internet access and the like,wherein a video signal is communicated via the downstream channel, whileonly control signals such as those associated with viewing of the videosignal are communicated via the upstream channel. Thus, the downstreamchannel requirement may exceed 1.5 Mbps, while the upstream channelrequirement may be as low as 16 Kbps.

In the future, it is expected that cable transmission in the upstreamdirection will become broader band, because digital televisiontransmission requires less bandwidth than analog televisiontransmission.

Each cable modem includes an upstream modulator for transmitting data tothe cable modem termination system and a downstream demodulator forreceiving data from the cable modem termination system. The upstreammodulator of each cable modem uses either QPSK or 16 QAM within the 5MHz to 42 MHz bandwidth of the upstream demodulator and the downstreamdemodulator of each cable modem utilizes either 64 QAM or 256 QAM in the54 MHz to 860 MHz bandwidth of the downstream modulator (in NorthAmerica).

Contemporary cable modem systems operate on a plurality of upstreamchannels and utilize time division multiple access (TDMA) in order tofacilitate communication between a plurality of cable modems and asingle cable modem termination system on each upstream channel.Typically, between 250 and 500 cable modems communicate with a singlecable modem termination system on a given upstream channel.

In order to accomplish TDMA for upstream communication, it is necessaryto assign time slots within which cable modems having a message to sendto the cable modem termination system are allowed to transmit. Theassignment of such time slots is accomplished by providing a requestcontention area in the upstream data path within which the cable modemsare permitted to contend in order to place a message which requestsadditional time in the upstream data path for the transmission of theirmessage. (Small data packets are sometimes also transmitted incontention regions.) The cable modem termination system responds tothese requests by assigning time slots to the cable modems making such arequest, so that as many of the cable modems as possible may transmittheir messages to the cable modem termination system utilizing TDMA andso that the transmissions are performed without undesirable collisions.

Because of the use of TDMA, the cable modem termination system must usea burst receiver, rather than a continuous receiver, to receive datapackets from cable modems via upstream communications. As those skilledin the art will appreciate, a continuous receiver can only be utilizedwhere generally continuous communications (as opposed to burstcommunications as in the present invention) are performed, so as tosubstantially maintain timing synchronization between the transmitterand the receiver, as is necessary for proper reception of thecommunicated information. During continuous communications, timingrecovery is a more straightforward process since signal acquisitiongenerally only occurs at the initiation of such communications. Thus,acquisition is generally only performed in continuous receivers once percontinuous transmission and each continuous transmission may be verylong.

However, the burst communications inherent to TDMA systems requireperiodic and frequent reacquisition of the signal. That is, during TDMAcommunications, the signal must be reacquired for each separate bursttransmission being received.

Since continuous receivers generally only acquire the signal once, theneed to minimize acquisition time is much less critical in continuousreceivers than in burst receivers, wherein acquisition must be performedfor each separate burst, and therefore occurs quite frequently. Thus,there is a strong motivation to minimize acquisition time in burstreceivers, so as to enhance overall data transmission efficiency andthroughput. As such, it is beneficial to provide techniques whichenhance the speed at which data packets transmitted according to TDMAmethodologies may be acquired by a burst receiver, such as that of acable modem termination system.

Referring now to FIG. 1, a hybrid fiber coaxial (HFC) network 10transmits data between a headend 12, which includes at least one cablemodem termination system, and a plurality of homes 14, each of whichcontains a cable modem. Such hybrid fiber coaxial networks are commonlyutilized by cable providers to provide Internet access, cabletelevision, pay-per-view and the like to subscribers.

Approximately 500 homes 14 are in electrical communication with eachnode 16, 34 of the hybrid fiber coaxial network 10, typically viacoaxial cable 29, 30, 31. Amplifiers 15 facilitate the electricalconnection of the more distant homes 14 to the nodes 16, 34 by boostingthe strength of the electrical signals so as to desirably enhance thesignal-to-noise ratio of such communications and by then transmittingthe electrical signals over coaxial conductors 30, 31. Coaxialconductors 29 electrically interconnect the homes 14 with the coaxialconductors 30, 31, which extend between amplifiers 15 and nodes 16, 34.

Each node 16, 34 is electrically connected to a hub 22, 24, typicallyvia an optical fiber 28, 32. The hubs 22, 24 are in communication withthe headend 12, via optical fiber 20, 26. Each hub is typically capablecommunicating with approximately 20,000 of homes 14.

The optical fiber 20, 26 extending intermediate the headend 12 and eachhub 22, 24 defines a fiber ring which is typically capable ofcommunicating between approximately 100,000 of homes 14 and the headend12.

The headend 12 may include video servers, satellite receivers, videomodulators, telephone switches and/or Internet routers 18, as well asthe cable modem termination system. The headend 12 communicates viatransmission line 13, which may be a T1 or T2 line, with the Internet,other headends and/or any other desired device(s) or network.

Referring now to FIG. 2, a simplified block diagram shows theinterconnection of the headend 12 and an exemplary home 14, wherein acable modem 46 communicates with a cable modem termination system atheadend 12, embodied as a line card 42, via hybrid fiber coaxial network(HFC) 10.

More particularly, a personal computer 48, disposed within the home 14,is connected via cable 11 to the cable modem 46 which communicates viacoaxial cable 17 with the hybrid fiber coaxial network 10. Network 10 inturn communicates via optical fiber 20 with the line card or cable modemtermination system (CMTS) 42 of the headend 12. Internet router 40permits communication between the headend 12 and the Internet or anyother desired device or network.

Reference is made to FIG. 3 for a depiction of the format of one type ofMAC header according to the Data-Over-Cable Service InterfaceSpecification (DOCSIS). Specifically, FIG. 3 depicts the format of abandwidth request. A field 60 (FC TYPE=11) identifies the header as abandwidth request frame. A field 61 (FC PARM=00010) specifies that it isa MAC header only, i.e., there are no following data PDU's. A field 62(EHDR_ON=0) signifies that it is not an extended header. A field 63(MAC_PARM) specifies the number of requested time slots. A field 64(SID) identifies the cable modem making the request. The bandwidthrequest format is explained in more detail in Table I, which follows:

TABLE I Field Usage Size FC FC_TYPE = 11; MAC-Specific 8 bits HeaderFC_PARM[4:0] = 00010; MAC Header only; no data PDU following EHDR_ON =0; No EHDR allowed MAC_PARM REQ, total number of minislots 8 bitsrequested SID Service ID (0 . . . 0x1FFF) 16 bits EHDR Extended MACHeader not allowed 0 bytes HCS MAC Header Check Sequence 2 bytes Lengthof a REQ MAC Header 6 bytes

Reference is made to FIG. 4 for a depiction of another type of format ofa MAC header according to the DOCSIS specification. Specifically, FIG. 4depicts an extended header capable of carrying a so-called “piggy-back”bandwidth request. In this case, field 60 (FC_TYPE=XX) identifies theheader as another type of MAC frame; field 61 (FC PARM=XXXXX) isdependent on the header type; field 62 (EHDR_ON=1) signifies that it isan extended header; and field 63 (MAC_PARM) specifies the length of theextended header plus optional data PDU in bytes. The extended headerformat is shown in more detail in Table II, which follows:

TABLE II Field Usage Size FC FC_TYPE = XX; Applies to all 8 bits MACHeaders FC_PARM[4:0} = XXXXX; dependent on FC_TYPE EHDR_ON = 1; EHDRpresent this example MAC_PARM ELEN = x; length of EHDR in 8 bits bytesLEN LEN = x + y; length of 16 bits EHDR plus OPTIONAL data PDU in bytesEHDR Extended MAC Header present this x bytes example HCS MAC HeaderCheck Sequence 2 bytes PDU OPTIONAL data PDU y bytes Length of MAC framewith EHDR 6 + x + y bytesExtended header (EHDR) field 65 in FIG. 4 contains the data fields shownin Table III, which follows:

TABLE III EH Element Fields Usage Size EH_TYPE EH element Type Field 4bits EH_LEN Length of EH_VALUE 4 bits EH_VALUE EH element data 0-15bytesThe various extended header types are shown in Table IV, which follows:

TABLE IV EH_TYPE EH_LEN EH_VALUE 0 0 Null configuration setting; may beused to pad the extended header. The EH_LEN MUST be zero, but theconfiguration setting may be repeated. 1 3 Request: mini-slots requested(1 byte); SID (2 bytes) 2 2 Acknowledgment requested; SID (2 bytes) 3 4Upstream Privacy EH Element (=BP_UP) 5 Upstream Privacy withFragmentation EH Element 4 4 Downstream Privacy EH Element (=BP_DOWN) 51 Service Flow EH Element; Payload Header Suppression Header 2 ServiceFlow EH Element; Payload Header Suppression Header (1 byte) UnsolicitedGrant Synchronization Header (1 byte) 6-9 Reserved 10-14 Reserved 15 XXExtended EH Element: EHX_TYPE (1 byte), EHX_LEN (1 byte), EH_VALUE(length determined by EHX_LEN)As shown in Tables III and IV, extended headers with piggy backbandwidth requests are designated EH_TYPE=0001 in a field EH_TYPE, thenumber of requested minislots and the requesting cable modem (SID) arecontained in a field EH_VALUE, and the length of the EH_VALUE field iscontained in a field EH_LEN.

Reference is made to FIG. 5, which illustrates how the inventionoperates to process some data types, particularly bandwidth requestsreceived, at a CMTS out of order on a priority basis to improve thequality of service of a cable modem system. Incoming data packetsreceived by the CMTS from cable modems are fed to a storage register 70.As represented symbolically by a switch 71 and a switch control 72, aheader monitor 73 reads the header of each data packet and makes adecision whether to route the data packet to a regular queue 74 or apriority queue 75. Header monitor 73 inspects header fields 60 and 62(FIGS. 3 and 4). If FC TYPE=11 in field 60, the packet is a bandwidthrequest so the entire packet is sent to priority queue 75. If EHDR_ON=1in field 62 and EH_TYPE=0001 in field 65, the packet contains apiggy-back request so the EH_VALUE containing the number of requestedminislots and the requesting cable modem (SID) and the EH_LEN containingthe length of the EH_VALUE are sent to priority queue 75; the remainderof the header and the appended PDUs are sent to regular queue 74. Packetdata units (PDU's) and messages other than bandwidth requests areidentified by monitor 73 because neither of the conditions set forth inthe preceding two sentences are present in the header; these data packetunits are sent to regular queue 74. Regular queue 74 is coupled to apacket processing unit 76 and priority queue 75 is coupled to abandwidth request processing unit 77, which generates bandwidthallocation MAPS for transmission downstream to the cable modems.Reference is made to application Ser. No. 09/57,4558 for a furtherdescription of the MAP generation process. In a typical embodiment ofthe invention, the packet and bandwidth request processing functions areperformed by software. FIG. 6 shows a CMTS at headend 12 (FIG. 2), whichincorporates the functionality described in connection with FIG. 5. In atypical embodiment, the components shown in FIG. 6 within a block 100all reside on a single integrated circuit chip and the other componentshown in FIG. 6 reside off chip 100. For the purpose of illustration,four upstream data channels are shown although more could be utilized.In each upstream data channel, a burst receiver 101 is coupled by a PHIinterface 102 to a prepare unit 103. Burst receivers 101 could, forexample, be BCM3138 burst receivers marketed by Broadcom Corporation. Asdescribed in application Ser. No. 09/574,558, data is transferredbetween burst receivers 101 and PHY interfaces in both directions.Preparse units 103 inspect the header of each packet to determine ifencryption was applied to the packet. Each preparse unit 103 is coupledby a decryptor (DES) unit 104 to a header processor 105. If encryptionwas applied to a packet the packet is decrypted in unit 104. A key RAMinterface unit 110 is connected from DES unit 104 to U-bus 107 for thispurpose. Each header processor 105 is coupled by a burst DMA unit 106 toan upstream U-bus 107. U-bus 107 is coupled by a RAM interface 108 to anexternal, i.e., off-chip, RAM 109, in which reassembly queues and DESkeys are stored. Burst DMA unit 106 assigns addresses to data packetsstored in RAM 109, checks the CRC, and adds control data to the datapackets stored in RAM 109 based on the header data. It also retrievesDES keys from RAM 109 response to key RAM interface unit 110. Atemporary reassembly memory engine 110 is also connected to upstreamU-bus 107. Reassembly engine 110 stores the received parts of fragmenteddata while the fragmented data is being reassembled into a PDU.Reference is made to application Ser. No. 09/574,558 for a descriptionof the fragmentation process. A PHS expansion and queue manager 111connects upstream U-bus 107 to an upstream U-bus 112. Reference is madeto application Ser. No. 09/652,861, filed on even date herewith by JohnD. Horton, Jr., entitled “Method and Apparatus for the Suppression ofPacket Headers” for a more detailed description of the PHS expansionprocess. U-bus 112 is connected by a RAM interface 113 to an externalRAM 114 in which PHS rules, output queues, and MIBs are stored.Reassembly unit 110 and manager 111 convert the data in the PDUs intostandard ethernet format and send such data via U-bus 112 to RAM 114until such data is called by an upstream egress engine 122.

Chip 100 has two data ports. One data port is a packet port 120 forexchanging PDUs with an ethernet network. The other data port is a PCIXbus interface unit (BUI) 121 through which data is exchanged with anexternal, i.e., off-chip processor (not shown). Thus, data stored inRAMs 109 and 114 is sent to and from the external processor throughinterface 121. The external processor performs the MAC functionsdescribed in application Ser. No. 09/574,558 and in the DOCSISspecification. Upstream egress engine 122 feeds PDUs to packet port 120and data messages to PCIX port 121 for transmission to the externalprocessor. U-bus 107 is coupled to PCIX port 121 by a PCI-to-U-busbridge 123 so as to form a control path between U-bus 112 and PCIX port121. Header processors 105 are each coupled to a request FIFO DMA unit125, which is in turn coupled by U-bus 112 to RAM 114. Unit 125 assignsaddresses in RAM 114 for storage of the bandwidth requests in a queueuntil the bandwidth requests are sent to the external processor togenerate the bandwidth allocation MAPS and sends these addresses to theexternal processor via bridge 123.

PCIX port 121 and packet port 120 are coupled by a downstream ingressengine 126 to a downstream U-bus 127. A RAM interface 128 couples U-bus127 to an external RAM 129, which stores downstream priority queues,packet header suppression rules, and DES keys and to an in-banddownstream queue manager 130. Queue manager 130 is coupled by a packetheader suppression unit 131 to a DOCSIS header creation unit 132. For adescription of header suppression unit 131 reference is made thepreviously mentioned application Ser. No. 09/652,861. DES, CRC, and HCSare appended to the data packets in a unit 137. Unit 137 is coupled by amap extractor FIFO 138 to a MPEG encapsulation unit 139 for transmissionin the downstream in-band data channel.

In the usual mode of operation, upstream egress engine 122 anddownstream ingress engine 128 control the transmission of the data theyprocess independent of the external processor.

A copy of the MAPs in FIFO 138 is also made for use in the CMTS. The MAPcopies are coupled to a MAP parser and overflow interface 140, whichfilters out what is not needed for use in the CMTS, leaving only the MAPinformation elements (IEs) needed in the CMTS to process signal burstreceived from the cable modems. These IEs are fed to a MAP FIFO 142. Ifthere are too many IEs to store in MAP FIFO 142, the overflow is storedtemporarily in RAM 129 for later retrieval. This gives the processormore flexibility to generate MAPs when the processing time is available.MAP FIFO 142 is coupled to PHY interfaces 102 to feed the IEs thereto.The IEs assist in identifying and demodulating the signal burstsreceived by burst receivers 101 as described in application Ser. No.09/574,558. U-bus 127 is also coupled by an SPI interface 143 to eachburst receiver 101. Burst receiver configuration information is sentthrough interface 143 to burst receivers 101 to configure them forreceipt of data transmitted by the cable modems as described inapplication Ser. No. 09/574,558.

Reference is made to application Ser. No. 09/653,155 (now U.S. Pat. No.6,760,316) filed by Anders Hebsgaard on even date herewith, entitled“Method and Apparatus for the Synchronization of Multiple Cable ModemTermination Devices” for a detailed description of a plurality of CMTSchips connected together so the same MAP information is shared by allthe CMTS chips and all the CMTS chips are synchronized to a master clockin one of the CMTS chips which is designated as a master CMTS. To thisend, MAP extractor FIFO 138 is also coupled to a master/slave interfaceunit 144 to send copies of the MAPs to slave CMTS chips such as slaveCMTS 160. An external master clock (not shown) is coupled to a MUX andtimestamp control unit 141, which is connected to a timestamp generationunit 145. Unit 141 is coupled to interface unit 144 to send timestampsto the slave CMTS chips to synchronize their operation to the masterclock. Generation unit 145 is coupled to an encapsulation unit 139 toembed time stamps in the in-band downstream data flow.

An external multiplexer 146 is fed to one input of an MPEG multiplexer147. Encapsulation unit 139 is fed to the other input of multiplexer147. Multiplexer 147 is coupled by a modulator interface 148 to anexternal downstream modulator 149, which could be, for example, aBCM3034 modulator marketed by Broadcom Corporation. Other content suchas graphics overlays could be introduced at the headend throughmultiplexer 146. To this end, multiplexer 146 is coupled to control unit141 to coordinate the merger of data from multiplexer 146 with the datafrom encapsulation unit 139. Control unit 141 is connected tomultiplexer 147 to control the selection of its inputs so only one inputis transmitted to modualtor interface 148. SPI interface 143 is alsocoupled to modulator 149 to supply configuration data thereto such asthe modulation type (e.g., QAM and symbol rate). Bridge 123 is coupledby an out-of-band generator 150 and a PHY interface 151 to a out-of-bandtransmitter 152, which could be for example, a BCM3037 modulatormarketed by Broadcom Corporation. SPI interface 143 is also coupled totransmitter 152 to supply configuration data thereto. Reference is madeto application Ser. No. 09/654,109, filed by Thomas J. Quigley on evendate herewith, entitled “Method and Apparatus for Latency Reduction inLow Power Two Way Communication Equipment Applications in Hibrid FiberCable Plants” for a detailed description of the out-of-band channel andits uses.

1. A cable modem termination system (CMTS), comprising: a receiver thatreceives data communications from one or more cable modems over anetwork; processing logic coupled to the receiver, the processing logicconfigured to process data communications that comprise bandwidthrequests out-of-order with respect to an order in which the datacommunications were received by the receiver; a first memory queuecoupled to the processing logic; and a second memory queue coupled tothe processing logic; wherein the processing logic analyzes the datacommunications received over the network to determine whether the datacommunications comprise bandwidth requests and wherein the processinglogic routes data communications that comprise bandwidth requests to thefirst memory queue and routes data communications that do not comprisebandwidth requests to the second memory queue.
 2. The CMTS of claim 1,wherein the processing logic is configured to process a datacommunication that comprises a bandwidth request ahead of anearlier-received data communication that comprises a packet data unit.3. The CMTS of claim 1, wherein the receiver comprises a burst receiver.4. The CMTS of claim 1, wherein the processing logic analyzes a headerfield associated with each data communication to determine whether thedata communication comprises a bandwidth request.
 5. The CMTS of claim1, further comprising: a storage register that stores datacommunications from the receiver; wherein the storage register isaccessible by the processing logic for analyzing the data communicationsstored therein.
 6. The CMTS of claim 1, further comprising: a bandwidthrequest processing unit coupled to the first memory queue, the bandwidthrequest processing unit configured to process bandwidth requests storedin the first memory queue to generate bandwidth allocation messages fortransmission to the one or more cable modems.
 7. The CMTS of claim 6,further comprising: a transmitter that transmits the bandwidthallocation messages to the one or more cable modems over the network. 8.The CMTS of claim 7, further comprising: a bandwidth allocation storageunit, wherein bandwidth allocation information from said bandwidthallocation messages are stored and are accessible to the receiver. 9.The CMTS of claim 7, further comprising: a master/slave interface unitconfigured to send bandwidth allocation information from said bandwidthallocation messages to one or more slave cable modem terminationsystems.
 10. The CMTS of claim 1, further comprising: a packetprocessing unit coupled to the second memory queue, the packetprocessing unit configured to process data packets stored in the secondmemory queue.
 11. The CMTS of claim 1, further comprising: a decryptordevice configured to decrypt incoming encrypted data communications,wherein the decryptor device is coupled to the receiver and to theprocessing logic; and a key interface wherein the key interface iscoupled to the decryptor, and is configured to provide keys fordecrypting said incoming encrypted data communications.
 12. The CMTS ofclaim 1, further comprising: a reassembly device coupled to thereceiver, wherein the reassembly device is configured to store receivedparts of a fragmented data communication, and wherein the processinglogic is further configured to reassemble the parts of the fragmenteddata communication.
 13. The CMTS of claim 1, wherein the processinglogic is further configured to generate bandwidth allocations based onthe data communications, and to transmit the bandwidth allocations to atleast one of the cable modems.
 14. A method, comprising: receiving datacommunications from one or more cable modems over a network; andprocessing, using at least one processor, data communications thatcomprise bandwidth requests out-of-order with respect to an order inwhich the data communications were received, wherein processing datacommunications that comprise bandwidth requests out-of-order withrespect to an order in which the data communications were receivedcomprises: analyzing the data communications received over the networkto determine whether the data communications comprise bandwidthrequests; routing data communications that comprise bandwidth requestsfor storage in a first memory queue; and routing data communicationsthat do not comprise bandwidth requests for storage in a second memoryqueue.
 15. The method of claim 14, wherein processing datacommunications that comprise bandwidth requests out-of-order withrespect to an order in which the data communications were receivedcomprises: processing a data communication that comprises a bandwidthrequest before processing an earlier-received data communication thatcomprises a packet data unit.
 16. The method of claim 14, whereinanalyzing the data communications received over the network to determinewhether the data communications comprise bandwidth requests comprisesanalyzing a header field associated with each data communication. 17.The method of claim 14, further comprising: storing the datacommunications received over the network in a storage register prior tothe analyzing step.
 18. The method of claim 14, further comprising:processing bandwidth requests stored in the first memory queue togenerate bandwidth allocation messages for transmission to the one ormore cable modems.
 19. The method of claim 18, further comprising:transmitting the bandwidth allocation messages to the one or more cablemodems over the network.
 20. The method of claim 19, further comprising:transmitting bandwidth allocation information from the bandwidthallocation messages to one or more slave cable modem terminationsystems.
 21. The method of claim 14, further comprising: processing datapackets stored in the second memory queue.
 22. A cable modem system,comprising: a plurality of cable modems; and a cable modem terminationsystem (CMTS) communicatively connected to the plurality of cable modemsover a network, the CMTS comprising: a receiver that receives datacommunications from the plurality of cable modems over the network;processing logic coupled to the receiver, the processing logicconfigured to process data communications that comprise bandwidthrequests out-of-order with respect to an order in which the datacommunications were received by the receiver; a first memory queuecoupled to the processing logic; and a second memory queue coupled tothe processing logic; wherein the processing logic analyzes the datacommunications received over the network to determine whether the datacommunications comprise bandwidth requests and wherein the processinglogic routes data communications that comprise bandwidth requests to thefirst memory queue and routes data communications that do not comprisebandwidth requests to the second memory queue.
 23. The cable modemsystem of claim 22 wherein the CMTS is configured to process a datacommunication that comprises a bandwidth request ahead of anearlier-received data communication that comprises a packet data unit.24. The cable modem system of claim 23 further comprising one or moreslave cable modem termination systems that are communicatively coupledto the cable modem termination system, wherein the slave cable modemtermination systems receive bandwidth allocation information from thecable modem termination system, and wherein the bandwidth allocationinformation is based on bandwidth allocation messages transmitted by thecable modem termination system to the plurality of cable modems.